Field
Embodiments described generally relate to paper or fiber products and wet strengthening agents for use in paper or fiber products. More particularly, such embodiments relate to wet strengthened paper or fiber products and wet strengthening resins that can include a polyamide-epihalohydrin (PAE) resin and a cationic styrene maleimide (SMI) resin.
Description of the Related Art
Paper is sheet material containing interconnected small, discrete fibers. The fibers are usually formed into a sheet on a fine screen from a dilute water suspension or slurry. Typically paper is made from cellulosic fibers, although occasionally synthetic fibers are used. The wet strength of paper is generally considered to be the resistance of the paper to rupture when wetted with water. Paper products made from untreated cellulose fibers generally lose their strength rapidly when they become wet, hence, they can be considered to have low wet strength. Generally, the wet strength of paper is only about 5% of the dry strength for the same type of paper. Various methods for treating paper products have been employed to overcome this disadvantage.
Wet strengthening agents can be added to the cellulose fibers of paper. There are many wet strengthening agents that have specific reactive groups capable of reacting with cellulosic fibers. Once the wet strengthening agent and cellulose fibers are combined, a curing mechanism provides a reinforcement of the inter-fibers hydrogen bonds and/or a protection against water penetration at the crossing points of the fibers. The strengthening effect of the wet strengthening agent usually depends on the cationic charge density, polymer molecular weight, specific hydrophilic-hydrophobic properties, and the reactivity of the wet strengthening agent.
Wet strengthening agents applied to paper are either of the “permanent” or “temporary” type, which are defined by how long the paper retains its wet strength after immersion in water. While wet strength retention is a desirable property in packaging materials, it presents a disposal problem because paper products having such properties generally require undesirably severe conditions to degrade. While some wet strengthening agents are known to impart temporary wet strength and thus would be suitable for sanitary or disposable paper uses, they often suffer from one or more drawbacks. For example, some wet strengthening agents generally have a low magnitude of wet strength (about one-half of the level achievable for permanent-type wet strengthening agents), are easily attacked by mold and slime, and/or can only be prepared as dilute solutions.
There is a need, therefore, for improved wet strengthened fiber products, wet strengthening resins, and methods for making the wet strengthened fiber products and the wet strengthening resins.